Electrical device having snap together housing parts

ABSTRACT

Electrical device having snap together housing parts, one part having a cylindrical outside surface formed with an annular projection to snap into an annular groove of a cylindrical inside surface of the other part. The projection and the groove have rounded cross-sectional shapes and the radius of curvature of the projection is greater than that of the groove, providing restricted areas interengaged with a high unit pressure to provide an effective seal. Impedance means are provided on one part in the form of an annular resistance element engaged by a wiper contact rotatable about the axis of the cylindrical surfaces and connected to a worm gear which is engaged by a worm on the other part when the parts are assembled.

United States Patent [72] Inventors Adoli' K. Scheiterbauer Munich; Helmut Stickdorn, Neubiberg Bavaria, both of Germany {21] Appl.No. 855,506 [22] Filed Sept.5, 1969 [45] Patented Nov. 2, 1971 [73] Assignee The Bunker-Ramo Corporation Oak Brook, Ill.

[54] ELECTRICAL DEVICE HAVING SNAP TOGETHER HOUSING PARTS 11 Claims, 5 Drawing Figs.

[52] U.S. Cl 338/164, 220/60, 338/DlG, l [5 1] Int. Cl H01c 9/02, HOlc 5/02 [50] Field of Search 338/118,

Primary Examiner- Lewis H. Myers Assistant Examiner-Gerald P. Tolin Attorney-Frederick M. Arbuckle ABSTRACT: Electrical device having snap together housing parts, one part having a cylindrical outside surface formed with an annular projection to snap into an annular groove of a cylindrical inside surface of the other part. The projection and the groove have rounded cross-sectional shapes and the radius of curvature of the projection is greater than that of the groove, providing restricted areas interengaged with a high unit pressure to provide an effective seal. Impedance means are provided on one part in the form of an annular resistance element engaged by a wiper contact rotatable about the axis of the cylindrical surfaces and connected to a worm gear which is engaged by a worm on the other part when the parts are assembled.

ELECTRICAL DEVICE HAVING SNAP TOGETHER HOUSING PARTS This invention relates to an electrical device and more particularly to an electrical device having snap together housing parts to facilitate rapid assembly while providing a highly effective seal, the device being readily and economically manufacturable.

The invention is illustrated herein as applied to small adjustable potentiometers but it will be understood that the principles of the invention are applicable to capacitors, inductors and other forms of electrical impedance devices. The assembly of prior art devices has required considerable time and has been otherwise difficult and expensive, especially where it is desired to provide a sealed housing for electrical impedances. By way of example, it has been the practice in the assembly of some devices to use cement and to hold parts clamped together until the cement sets, which requires a considerable amount of time and care.

This invention was evolved with the general object of overcoming disadvantages of prior arrangements and of providing a device which can be readily and quickly assembled while an effective seal is obtained.

Another object of the invention is to provide a device which is durable while being readily and economically manufacturable.

According to this invention, first and second housing parts are provided, the first part having a chamber and an opening to the chamber while the second part has impedance means supported thereon and positioned in the chamber, the second part having a generally cylindrical outside surface snap fitted in sealed relation into a generally cylindrical inside surface of the first part.

According to a specific of the invention, one of the generally cylindrical surfaces has an annular projection adapted to snap into an annular groove formed in the other.

Another specific feature is in the formation of the groove and the projection with rounded cross-sectional shapes to facilitate assembly, preferably with the projection before assembly having a radius of curvature substantially greater than that of the groove before assembly such that upon assembly side portions of the groove of restricted areas are interengaged with the projection to obtain a high pressure per unit area and a highly effective seal.

A further specific feature relates to the provision of a tapered generally frustoconical portion on one end of one of the surfaces to facilitate assembly.

Still another feature of the invention relates to the combination of the snap together feature with an impedance adjustment arrangement wherein coupling means are interengaged upon assembly of the parts to connect a movable control element associated with the impedance means with a manually adjustable element on the other part, controllable from the outside thereof. Preferably, the control element is in the form of a worm gear rotatable about the axis of the cylindrical surfaces, the manually adjustable element is in the form of a rotatable shaft member having one end accessible for actuation from the outside and the coupling means is in the form of a worm on the opposite end of the rotatable member meshed with the worm gear in the assembled condition of the parts. The worm gear is journaled about the axis of the generally cylindrical surfaces and is preferably connected directly to a wiper contact engaged with a resistance element extending arcuately about the axis of rotation.

This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate a preferred embodiment and in which:

FIG. I is a bottom plan view of a potentiometer unit having a snap together housing and constructed in accordance with the principles ofthis invention;

FIG. 2 is a sectional view, on an enlarged scale, taken substantially along line lI-ll ofFIG. l;

FIG. 3 is a greatly enlarged cross-sectional view showing the relationship of a groove and a projection with the parts positioned in an initial step of assembly;

FIG. 4 is a view similar to FIG. 3, showing the relationship of the groove and the projection after assembly; and

FIG. 5 is a top plan view of the potentiometer unit, with parts broken away to show the internal construction.

Reference numeral 10 generally designates a potentiometer unit constructed in accordance with the principles of this invention. The unit 10 comprises a first housing part 11 having a chamber 12 therewithin and a second housing part 13 with impedance means being supported on the second part 13 to be positioned in the chamber 12, the impedance means being in the form of an arcuately extending resistance element 14 engaged by a rotatable wiper contact 15, the angular position of the contact 15 being adjustable by means of a manual adjustment element 16, projecting from the outside of the housing part 11. The adjustment mechanism is described in detail hereinafter. The contact 15 and end tenninals of the resistance element 14 are connected to terminal prongs l7, l8 and 19 projecting in parallel relation from the housing part 13, for connection of the unit in a circuit in which it is to be used.

In accordance with this invention, the part 11 has an opening to the chamber 12 which has a generally cylindrical inside surface 21 and the part 13 has a generally cylindrical outside surface 22 which is snap fitted in sealed relation into the surface 21. According to a specific feature, the surface 21 is formed with an annular groove 23 therein and the surface 22 is formed with an annular projection 24 which snaps into the groove 23 when the parts are assembled. If desired, the surface 21 could be formed with a projection and the surface 22 with a groove although the illustrated arrangement is preferred in facilitating formation of the parts.

According to another specific feature, the surface 21 is formed with a tapered generally frustoconical portion 25 at the entrant end thereof to facilitate alignment of the parts and entry of the annular projection 14 into the groove 23 in assembly. A cylindrical surface portion 26 may preferably be provided between the inner end of the portion 25 and the groove 23.

Important features relate to the form of the groove 23 and the projection 24 and to the relative dimensioning thereof, to facilitate assembly and to obtain a highly effective seal. In particular, the groove 23 and the projection 24 have concavely and convexly rounded cross-sectional shapes which facilitates assembly of the parts. Thus as shown in FIG. 3 when the parts are being assembled, the rounded outer surface of the projection 24 engages the tapered surface 25 and as the part 13 is moved into the part 11, a wedging or jamming action takes place in which the inside surface 21, at the portion 26, is deformed outwardly while the projection 24 is deformed inwardly. In addition, as diagrammatically indicated in FIG. 3, the radius of curvature of the groove 23, designated by R,, is less than the radius of curvature of the projection 24, designated by R As a result, when the parts are snapped into assembly, side portions of the groove 23 are engaged with side portions of the projection 24 only at restricted areas designated by reference numerals 27 and 28, at which a very high pressure per unit area is obtained, so as to obtain a highly effective seal. It should be noted that the effective width of the groove 23 should be substantially less than twice the radius of curvature thereof to obtain the desired relationship of the parts. It is also noted that the inside surface 21, moves inwardly with respect to the groove 23 and includes a cylindrical portion 29 which may preferably have a diameter equal to that of the portion 26 while the surface 22 includes a cylindrical portion 30 in facing relation to the portion 29 when the parts are assembled, the portion 30 preferably having a diameter less than that of the portion 29.

In accordance with a further feature of the invention, the assembly of the parts results in a mechanical interconnection between the element 16 and the contact 15. Referring to FIG. 5, the element 16 is the form of a shaft journaled in a passage 32 in the part 11 for rotation therein. A cross pin 33 is inserted after disposing of the element 16 in the passage 32 to extend into an annular groove 34 in the element 16 and to retain the element 16 against axial displacement while permitting rotation thereof. The element 16 has a second groove 35 in which an O-ring seal member 36 is disposed to provide a seal.

On the end of the element 16 which projects from the housing part 11, a slot 38 is provided for engageability by a screwdriver blade or the like. Toward the opposite end of the element 16, a helical thread 39 is formed to define a worm which is meshed with the teeth on the periphery of a worm gear 40 journaled within the chamber 12 for rotation about the axis of the generally cylindrical surfaces 21 and 22. The worm gear 40 is journaled on a sleeve 41 which is fitted onto a stud 42 formed integrally with the part 13. The worm gear 40 is provided with grooves or recesses 43 which interlock with projecting portions 44 of a specially formed member 45 of resilient sheet metal. Member 45 is bent to provide two portions 46 and 47 in spaced parallel planes transverse to the axis of rotation of the gear 40, the projections 44 being formed integrally with the portion 46 which is engaged with a central portion of the gear 40 and the portion 47 being engaged with an enlarged diameter flange portion 48 of the sleeve 41. A slot 50 is formed in the member 47 which extends generally arcuately around the portion 46, through approximately 270, to define a generally U-shaped portion 51 the ends of the legs of which are integrally connected to the portion 46 with the wiper contact being formed as an integral extension of the center of the bight of the portion 51. The portion 51 is so bent as to obtain a certain pressure engagement between the contact 51 and the resistance means element 14. The terminal prong 17 is formed with a radially inwardly extending portion 53 which is engaged with the sleeve 41 to obtain an electrical connection to the contact 15, the sleeve 41 being of metal. An end terminal 54 of the resistance element 14 is connected in a similar fashion to the terminal prong 18 and another similar connection is provided between an opposite end terminal of the resistance element 14 and the terminal prong 19.

Both the part 13 and the part 11 are preferably formed of a thermoplastic material and the prongs 17-19 are so molded or fitted into the part 13 as to obtain a seal. It is noted that in the assembly of the parts, the teeth of the gear 40 may be meshed with the teeth of the worm 39 when the part 13 is initially inserted into the opening defined by the surface 21, i.e. when the parts are in relative positions as represented in FIG. 3, after which the part 13 is forced into place with the snap engagement of the projection 24 into the groove 23.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

We claim as our invention:

1. In an electrical device, a housing comprising first and second parts, said first part having a chamber and an opening to said chamber, impedance means supported on said second part and positioned in said chamber, impedance means supported on said second part and positioned in said chamber, said second part having an effective cross-sectional area substantially less than the effective area of said opening, said opening having an inside surface and said second part having an outside surface, one of said surfaces having a groove of a given effective width and the other one of said surfaces having a projection of a given effective width substantially greater than said given width of said groove and snap fitted partially within said groove into engagement with opposite side portions thereof only along a pair of unbroken continuous lines of interengagement between said opposite side portions of said groove and opposite side portions of said projection to obtain a high pressure per unit area and an effective seal, said groove having a given effective depth and said projection having a given effective height substantially less than said given depth to provide a clearance space between said groove and the unen aged ortion of said projection within said groove.

2. n an e ectrrcal device as defined in claim 1, wherein said surfaces are generally cylindrical in shape, said groove being an annular groove and said projection being an annular projection.

3. In an electrical device as defined in claim 2, said groove and projection having concavely and convexly rounded crosssectional shapes.

4. In an electrical device as defined in claim 3, said projection having a radius of curvature substantially greater than that of said groove and being interengaged with side portions of said groove of restricted area to obtain a high pressure per unit area and an effective seal.

5. In an electrical device as defined in claim 2, said one of said generally cylindrical surfaces including a tapered generally frustoconical portion at one end to facilitate alignment of the part and entry of said annular projection into said annular groove in assembly.

6. In an electrical device as defined in claim 2, said annular groove being provided in said generally cylindrical inside surface of said first part and said annular projection being provided on said generally cylindrical outside surface of said second part.

7. In an electrical device as defined in claim 1, a movable control element associated with said impedance means for controlling the impedance thereof, a manually adjustable element on said first part manually controlled from the outside thereof, and coupling means connected to said manual adjustment element and engaged with said control element in the assembled condition of said parts.

8. In an electrical device as defined in claim 7, said control element being in the form of a worm gear, said manually adjustable element being in the form of a rotatable shaft member having one end accessible for actuation from the outside of said first part, and said coupling means being in the form ofa worm on the opposite end portion of said rotatable member meshed with said worm gear in the initial assembly of said parts.

9. In an electrical device as defined in claim 8, said worm gear being journaled about the axis of said generally cylindrical surfaces.

10. In an electrical device as defined in claim 1, said impedance means comprising a resistance element extending arcuately about the axis ofsaid generally cylindrical surface, and a wiper contact engaged with said resistance element and supported for rotation about said axis.

11. In an electrical device as defined in claim 10, said second part being of a molded plastic material and terminal prongs projecting from the outside of said second part and having ends electrically connected to said wiper contact and said resistance element. 

1. In an electrical device, a housing comprising first and second parts, said first part having a chamber and an opening to said chamber, impedance means supported on said second part and positioned in said chamber, impedance means supported on said second part and positioned in said chamber, said second part having an effective cross-sectional area substantially less than the effective area of said opening, said opening having an inside surface and said second part having an outside surface, one of said surfaces having a groove of a given effective width and the other one of said surfaces having a projection of a given effective width substantially greater than said given width of said groove and snap fitted partially within said groove into engagement with opposite side portions thereof only along a pair of unbroken continuous lines of interengagement between said opposite side portions of said groove and opposite side portions of said projection to obtain a high pressure per unit area and an effective seal, said groove having a given effective depth and said projection having a given effective height substantially less than said given depth to provide a clearance space between said groove and the unengaged portion of said projection within said groove.
 2. In an electrical device as defined in claim 1, wherein said surfaces are generally cylindrical in shape, said groove being an annular groove and said projection being an annular projection.
 3. In an electrical device as defined in claim 2, said groove and projection having concavely and convexly rounded cross-sectional shapes.
 4. In an electrical device as defined in claim 3, said projection having a radius of curvature substantially greater than that of said groove and being interengaged with side portions of said groove of restricted area to obtain a high pressure per unit area and an effective seal.
 5. In an electrical device as defined in claim 2, said one of said generally cylindrical surfaces including a tapered generally frustoconical portion at one end to facilitate alignment of the part and entry of said annular projection into said annular groove in assembly.
 6. In an electrical device as defined in claim 2, said annular groove being provided in said generally cylindrical inside surface of said first part and said annular projection being provided on said generally cylindrical outside surface of said second part.
 7. In an electrical device as defined in claim 1, a movable control element associated with said impedance means for controlling the impedance thereof, a manually adjustable element on said first part manually controlled from the outside thereof, and coupling means connected to said manual adjustment element and engaged with said control element in the assembled condition of said parts.
 8. In an electrical device as defined in claim 7, said control element being in the form of a worm gear, said manually adjustable element being in the form of a rotatable shaft member having one end accessible for actuation from the outside of said first part, and said coupling means being in the form of a worm on the opposite end portion of said rotatable member meshEd with said worm gear in the initial assembly of said parts.
 9. In an electrical device as defined in claim 8, said worm gear being journaled about the axis of said generally cylindrical surfaces.
 10. In an electrical device as defined in claim 1, said impedance means comprising a resistance element extending arcuately about the axis of said generally cylindrical surface, and a wiper contact engaged with said resistance element and supported for rotation about said axis.
 11. In an electrical device as defined in claim 10, said second part being of a molded plastic material and terminal prongs projecting from the outside of said second part and having ends electrically connected to said wiper contact and said resistance element. 